[Mesa-dev] [PATCH] i965: Delete most of the linked GLSL IR when using NIR.

[Tapani Pälli]

On 05/06/2015 04:57 AM, Kenneth Graunke wrote:
> Vertex shader attribute and fragment shader output queries rely on being
> able to inspect top-level ir_variable objects.  So, we have to keep
> those.  However, functions and global temporary variables can be deleted
> with impunity.
>
> Saves 58MB of memory when replaying a Dota 2 trace on Broadwell.
>
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>   src/mesa/drivers/dri/i965/brw_shader.cpp | 43 +++++++++++++++++++++++++++++++-
>   1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
> index c1fd859..6e4abb2 100644
> --- a/src/mesa/drivers/dri/i965/brw_shader.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
> @@ -138,6 +138,45 @@ brw_lower_packing_builtins(struct brw_context *brw,
>      lower_packing_builtins(ir, ops);
>   }
>
> +static bool
> +is_vert_input_or_frag_output(gl_shader_stage stage, ir_variable *var)

I believe you'll need to save any input and output independent of shader 
stage as with GL_ARB_program_interface_query application can query if 
some input or output is referenced by a given stage. Did you encounter 
any failures on Piglit tests?

I've been working to get rid of ir_variable on the background but it has 
taken a bit of time as there seems to be always something else to be 
worked first 'priority wise' ... but I think this is a nice start 
anyways to get rid of most IR in memory.

> +{
> +   if (var) {
> +      if (stage == MESA_SHADER_VERTEX) {
> +         return var->data.mode == ir_var_shader_in ||
> +                var->data.mode == ir_var_system_value;
> +      }
> +
> +      if (stage == MESA_SHADER_FRAGMENT) {
> +         return var->data.mode == ir_var_shader_out;
> +      }
> +   }
> +   return false;
> +}
> +
> +/**
> + * Delete GLSL IR except for VS inputs and FS outputs.
> + *
> + * Once we've translated to NIR, we don't need most of the linked GLSL IR anymore.
> + * However, GL API calls for introspecting certain shader inputs/outputs
> + * (shader_query.cpp) require us to keep some top-level ir_variables.
> + */
> +static void
> +delete_most_glsl_ir(struct gl_shader *shader)
> +{
> +   void *mem_ctx = ralloc_context(NULL);
> +   ralloc_adopt(mem_ctx, shader->ir);
> +
> +   foreach_in_list_safe(ir_instruction, ir, shader->ir) {
> +      if (!is_vert_input_or_frag_output(shader->Stage, ir->as_variable()))
> +         ir->remove();
> +   }
> +
> +   reparent_ir(shader->ir, shader->ir);
> +   ralloc_free(mem_ctx);
> +}
> +
> +
>   static void
>   process_glsl_ir(struct brw_context *brw,
>                   struct gl_shader_program *shader_prog,
> @@ -297,8 +336,10 @@ brw_link_shader(struct gl_context *ctx, struct gl_shader_program *shProg)
>
>         brw_add_texrect_params(prog);
>
> -      if (options->NirOptions)
> +      if (options->NirOptions) {
>            prog->nir = brw_create_nir(brw, shProg, prog, (gl_shader_stage) stage);
> +         delete_most_glsl_ir(shader);
> +      }
>
>         _mesa_reference_program(ctx, &prog, NULL);
>      }
>